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Abstract
OBJECTIVE Whereas numerous experimental and clinical studies suggest a complex involvement of serotonin in the regulation of anxiety, it remains to be clarified if the dominating impact of this transmitter is best described as anxiety-reducing or anxiety-promoting. The aim of this study was to assess the impact of serotonin depletion on acquisition, consolidation, and expression of conditioned fear. METHODS Male Sprague-Dawley rats were exposed to foot shocks as unconditioned stimulus and assessed with respect to freezing behaviour when re-subjected to context. Serotonin depletion was achieved by administration of a serotonin synthesis inhibitor, para-chlorophenylalanine (PCPA) (300 mg/kg daily × 3), (i) throughout the period from (and including) acquisition to (and including) expression, (ii) during acquisition but not expression, (iii) after acquisition only, and (iv) during expression only. RESULTS The time spent freezing was significantly reduced in animals that were serotonin-depleted during the entire period from (and including) acquisition to (and including) expression, as well as in those being serotonin-depleted during either acquisition only or expression only. In contrast, PCPA administrated immediately after acquisition, that is during memory consolidation, did not impact the expression of conditioned fear. CONCLUSION Intact serotonergic neurotransmission is important for both acquisition and expression of context-conditioned fear.
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Effects of Selective Serotonin Reuptake Inhibitors on the Shock-Induced Ultrasonic Vocalization of Rats in Different Experimental Designs. ACTA ACUST UNITED AC 2018. [DOI: 10.1016/b978-0-12-809600-0.00029-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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3
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Fritze S, Spanagel R, Noori HR. Adaptive dynamics of the 5-HT systems following chronic administration of selective serotonin reuptake inhibitors: a meta-analysis. J Neurochem 2017; 142:747-755. [PMID: 28653748 DOI: 10.1111/jnc.14114] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 06/20/2017] [Accepted: 06/20/2017] [Indexed: 02/05/2023]
Abstract
Selective serotonin reuptake inhibitors (SSRIs) are the most frequently prescribed antidepressants. However, a major concern is their delayed onset of action, which is hypothesized to be associated with the time required for serotonin (5-HT) autoreceptors to desensitize, which should be reflected by actual neurochemical changes. Numerous in vivo microdialysis studies have been published that report on 5-HT levels in different brain sites following SSRI administration. Here, we performed a meta-analysis on dynamic changes of 5-HT neurotransmission during the course of chronic SSRI treatment. We conducted a meta-analysis on research articles of 5-HT neurotransmission measured by in vivo microdialysis in rat brain after subchronic and chronic SSRI administrations. In total, data from 42 microdialysis studies (798 rats) were analyzed. Within the first week of SSRI treatment, extracellular 5-HT concentrations drop in frontal cortex. Over the next 2 weeks of treatment, a linear increase in extracellular 5-HT levels up to 350% of prior treatment baseline is evident (n = 269). However, in hippocampus, prefrontal cortex, nucleus accumbens, and ventral tegmental area we found increased 5-HT levels within the first 3 days of SSRI administration. The time course of 5-HT dynamics in frontal cortex is in line with the hypothesis that 5-HT autoreceptors desensitize over 2-3 weeks of SSRI treatment and thereby enhanced extracellular 5-HT levels ensue. Yet, in other regions we did not find evidence supporting the traditional autoreceptor-mediated feedback loops hypothesis and thus other neurobiological adaptation mechanisms may also play a role in the delayed onset of SSRI action.
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Affiliation(s)
- Stefan Fritze
- Institute of Psychopharmacology, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Rainer Spanagel
- Institute of Psychopharmacology, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Hamid R Noori
- Institute of Psychopharmacology, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.,Neuronal Convergence Group, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
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Kaneko F, Kawahara Y, Kishikawa Y, Hanada Y, Yamada M, Kakuma T, Kawahara H, Nishi A. Long-Term Citalopram Treatment Alters the Stress Responses of the Cortical Dopamine and Noradrenaline Systems: the Role of Cortical 5-HT1A Receptors. Int J Neuropsychopharmacol 2016; 19:pyw026. [PMID: 27029212 PMCID: PMC5006198 DOI: 10.1093/ijnp/pyw026] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Accepted: 03/23/2016] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Cortical dopamine and noradrenaline are involved in the stress response. Citalopram, a selective serotonin reuptake inhibitor, has direct and indirect effects on the serotonergic system. Furthermore, long-term treatment with citalopram affects the dopamine and noradrenaline systems, which could contribute to the therapeutic action of antidepressants. METHODS The effects of long-term treatment with citalopram on the responses of the dopamine and noradrenaline systems in the rat prefrontal cortex to acute handling stress were evaluated using in vivo microdialysis. RESULTS Acute handling stress increased dopamine and noradrenaline levels in the prefrontal cortex. The dopamine and noradrenaline responses were suppressed by local infusion of a 5-HT1A receptor agonist, 7-(Dipropylamino)-5,6,7,8-tetrahydronaphthalen-1-ol;hydrobromide, into the prefrontal cortex. The dopamine response was abolished by long-term treatment with citalopram, and the abolished dopamine response was reversed by local infusion of a 5-HT1A receptor antagonist, (Z)-but-2-enedioic acid;N-[2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-pyridin-2-ylcyclohexanecarboxamide into the prefrontal cortex. On the other hand, long-term treatment with citalopram reduced the basal noradrenaline levels (approximately 40% of the controls), but not the basal dopamine levels. The noradrenaline response was maintained despite the low basal noradrenaline levels. Signaling from the 5-HT1A receptors and α2-adrenoceptors was not involved in the decrease in the basal noradrenaline levels but partially affected the noradrenaline response. CONCLUSIONS Chronic citalopram treatment differentially suppresses the dopamine and noradrenaline systems in the prefrontal cortex, and the dopamine stress response was preferentially controlled by upregulating 5-HT1A receptor signaling. Our findings provide insight into how antidepressants modulate the dopamine and noradrenaline systems to overcome acute stress.
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Affiliation(s)
| | - Yukie Kawahara
- Department of Pharmacology, Kurume University School of Medicine, Kurume, Fukuoka, Japan (Ms Kaneko and Drs Kawahara, Kishikawa, Hanada, and Nishi); Department of Psychiatry, Tokyo Women's Medical University, Shinjuku-ku, Tokyo, Japan (Dr Yamada); Biostatistics Center, Kurume University, Kurume, Fukuoka, Japan (Dr Kakuma); Department of Dental Anesthesiology, School of Dentistry, Tsurumi University, Tsurumi-ku, Yokohama, Kanagawa, Japan (Dr Kawahara).
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Noradrenergic blockade stabilizes prefrontal activity and enables fear extinction under stress. Proc Natl Acad Sci U S A 2015; 112:E3729-37. [PMID: 26124100 DOI: 10.1073/pnas.1500682112] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Stress-induced impairments in extinction learning are believed to sustain posttraumatic stress disorder (PTSD). Noradrenergic signaling may contribute to extinction impairments by modulating medial prefrontal cortex (mPFC) circuits involved in fear regulation. Here we demonstrate that aversive fear conditioning rapidly and persistently alters spontaneous single-unit activity in the prelimbic and infralimbic subdivisions of the mPFC in behaving rats. These conditioning-induced changes in mPFC firing were mitigated by systemic administration of propranolol (10 mg/kg, i.p.), a β-noradrenergic receptor antagonist. Moreover, propranolol administration dampened the stress-induced impairment in extinction observed when extinction training is delivered shortly after fear conditioning. These findings suggest that β-adrenoceptors mediate stress-induced changes in mPFC spike firing that contribute to extinction impairments. Propranolol may be a helpful adjunct to behavioral therapy for PTSD, particularly in patients who have recently experienced trauma.
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Treatment of cognitive dysfunction in major depressive disorder—a review of the preclinical evidence for efficacy of selective serotonin reuptake inhibitors, serotonin–norepinephrine reuptake inhibitors and the multimodal-acting antidepressant vortioxetine. Eur J Pharmacol 2015; 753:19-31. [DOI: 10.1016/j.ejphar.2014.07.044] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 06/06/2014] [Accepted: 07/24/2014] [Indexed: 02/02/2023]
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Lee B, Sur B, Kwon S, Yeom M, Shim I, Lee H, Hahm DH. Chronic administration of catechin decreases depression and anxiety-like behaviors in a rat model using chronic corticosterone injections. Biomol Ther (Seoul) 2013; 21:313-22. [PMID: 24244817 PMCID: PMC3819905 DOI: 10.4062/biomolther.2013.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 06/03/2013] [Accepted: 06/07/2013] [Indexed: 12/17/2022] Open
Abstract
Previous studies have demonstrated that repeated administration of the exogenous stress hormone corticosterone (CORT) induces dysregulation in the hypothalamic-pituitary-adrenal (HPA) axis and results in depression and anxiety. The current study sought to verify the impact of catechin (CTN) administration on chronic CORT-induced behavioral alterations using the forced swimming test (FST) and the elevated plus maze (EPM) test. Additionally, the effects of CTN on central noradrenergic systems were examined by observing changes in neuronal tyrosine hydroxylase (TH) immunoreactivity in rat brains. Male rats received 10, 20, or 40 mg/kg CTN (i.p.) 1 h prior to a daily injection of CORT for 21 consecutive days. The activation of the HPA axis in response to the repeated CORT injections was confirmed by measuring serum levels of CORT and the expression of corticotrophin-releasing factor (CRF) in the hypothalamus. Daily CTN administration significantly decreased immobility in the FST, increased open-arm exploration in the EPM test, and significantly blocked increases of TH expression in the locus coeruleus (LC). It also significantly enhanced the total number of line crossing in the open-field test (OFT), while individual differences in locomotor activities between experimental groups were not observed in the OFT. Taken together, these findings indicate that the administration of CTN prior to high-dose exogenous CORT significantly improves helpless behaviors, possibly by modulating the central noradrenergic system in rats. Therefore, CTN may be a useful agent for the treatment or alleviation of the complex symptoms associated with depression and anxiety disorders.
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Affiliation(s)
- Bombi Lee
- Acupuncture and Meridian Science Research Center
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Fucoidan prevents depression-like behavior in rats exposed to repeated restraint stress. J Nat Med 2012; 67:534-44. [PMID: 23090005 DOI: 10.1007/s11418-012-0712-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Accepted: 09/29/2012] [Indexed: 10/27/2022]
Abstract
Previous studies have demonstrated that repeated restraint stress in rodents increased depression-like behavior and altered the expression of corticotrophin-releasing factor in the hypothalamus. The current study focused on verifying the impact of fucoidan (FCN) administration on repeated restraint stress-induced behavioral responses using the forced swimming test (FST). Additionally, we examined the effect of FCN on the central noradrenergic system by observing changes in neuronal tyrosine hydroxylase (TH) immunoreactivity and brain-derived neurotrophic factor (BDNF) mRNA expression in the rat brains. Male rats received 10, 20, or 50 mg/kg FCN (i.p.) 30 min before daily exposures to repeated restraint stress (2 h/day) for 14 days. Repeated restraint stress increased immobility in the FST. Daily administration of FCN during the repeated restraint stress period significantly inhibited the stress-induced behavioral deficits in this behavioral test. Administration of FCN also significantly blocked the increase in TH expression in the locus coeruleus and the basolateral nucleus of the amygdala, and the decrease in BDNF mRNA expression in the hippocampus. Taken together, these findings indicate that administration of FCN prior to restraint stress significantly improved helpless behavior in rats, possibly through modulating the central noradrenergic system. Therefore, FCN may be a useful agent for treating complex symptoms of depression disorder.
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Kassai F, Gyertyán I. Shock priming enhances the efficacy of SSRIs in the foot shock-induced ultrasonic vocalization test. Prog Neuropsychopharmacol Biol Psychiatry 2012; 36:128-35. [PMID: 22041499 DOI: 10.1016/j.pnpbp.2011.10.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2011] [Revised: 10/04/2011] [Accepted: 10/18/2011] [Indexed: 11/30/2022]
Abstract
Data on the effect of acutely administered serotonin reuptake inhibitors (SSRIs) in animal anxiety models have been inconsistent. In some of the models these compounds showed anxiolytic properties, while in others they were ineffective or even anxiogenic. In the foot shock-induced ultrasonic vocalization (USV) test in the adult rat, SSRIs were reported to be effective, however, they were only tested with protocols using multiple shocking design. In the present study, anxiolytic effects of various SSRI compounds (sertraline, fluoxetine, paroxetine, escitalopram) were tested in three distinct USV test protocols in comparison with alprazolam and 8-OH-DPAT. In the single shocking protocol, animals were exposed to one shocking session after the drug treatment. In the multiple shocking protocol, rats went through a foot shock priming session before each drug test. On priming days animals received foot shocks without drug treatment. On the test day (the day after), rats received drug treatment and then were shocked again. In the context conditioning protocol animals were exposed to foot shocks on two consecutive days before the drug test. On the third, test day, after drug treatment animals were replaced to the shocking chamber, but this time shocks were not delivered. SSRIs were ineffective using the single shocking protocol. In the context conditioned protocol, all SSRIs showed linear dose-response relationship with ED50 values of 8.5, 2.2, 0.77 and 0.93 mg/kg i.p. for fluoxetine, sertraline, paroxetine and escitalopram, respectively. Using the multiple shocking protocol, SSRIs were only partially effective with maximum inhibitions ranging between 44% and 62%. In contrast to SSRIs, the benzodiazepine anxiolytics, alprazolam showed anxiolytic activity with linear dose-response relationship in all of the test protocols, with ED50 values varying from 1.3 to 4.0 mg/kg i.p. The serotonin 5HT1A receptor antagonist 8-OH-DPAT also showed linear dose-response relationship in all protocols, but this compound was less potent in the single shocking design (ED50 values were 0.27, 0.04 and 0.07 mg/kg i.p. in the single shocking, multiple shocking and context conditioned protocol, respectively). In conclusion, our results show that priming has a major impact on the effectiveness of SSRIs in the USV test, and the three test protocols applied in this study have different predictive and face validity.
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Affiliation(s)
- Ferenc Kassai
- Department of Behavioral Pharmacology, Gedeon Richter Plc., Hungary.
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McEuen JG, Semsar KA, Lim MA, Bale TL. Influence of sex and corticotropin-releasing factor pathways as determinants in serotonin sensitivity. Endocrinology 2009; 150:3709-16. [PMID: 19342454 PMCID: PMC2717884 DOI: 10.1210/en.2008-1721] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Stress sensitivity and sex are predictive factors in affective disorder susceptibility. Serotonin (5-HT) pathway recruitment by corticotropin-releasing factor (CRF) during stress is necessary in adaptive coping behaviors, but sex differences in such responses have not been investigated. Using selective 5-HT reuptake inhibitor (SSRI) administration to acutely elevate 5-HT in a genetic model of stress sensitivity, we examined behavioral and physiological responses in male and female stress-sensitive CRF receptor-2-deficient (R2KO) mice. Chronic SSRI treatment was used to confirm outcomes were specific to acute 5-HT elevation and not antidepressant efficacy. We hypothesized that R2KO mice would show a greater sensitivity to acute changes in 5-HT and that, because females typically are more stress sensitive, R2KO females would be the most responsive. Our results supported this hypothesis because females of both genotypes and R2KO males showed a greater sensitivity to an acute 10 mg/kg dose of citalopram in a tail suspension test, displaying decreased immobile time and increased latency to immobility. Furthermore, acute citalopram promoted significant anxiogenic-like effects that were specific to R2KO females in the elevated plus maze and light-dark box tests. Chronic citalopram did not produce these behavioral changes, supporting specificity to acute 5-HT modulation. Mechanistically, females had decreased hippocampal 5-HT transporter (SERT) levels, whereas R2KO mice showed reduced SERT in the prefrontal cortex, supporting a possible intersection of sex and genotype where R2KO females would have the lowest SERT to be blocked by the SSRI. This sensitivity to 5-HT-mediated anxiety in females may underlie a heightened vulnerability to stress-related affective disorders.
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Affiliation(s)
- Jonathan G McEuen
- Department of Animal Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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Fitzgerald PJ. Is norepinephrine an etiological factor in some types of cancer? Int J Cancer 2009; 124:257-63. [DOI: 10.1002/ijc.24063] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Mueller D, Porter JT, Quirk GJ. Noradrenergic signaling in infralimbic cortex increases cell excitability and strengthens memory for fear extinction. J Neurosci 2008; 28:369-75. [PMID: 18184779 PMCID: PMC6670514 DOI: 10.1523/jneurosci.3248-07.2008] [Citation(s) in RCA: 217] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Revised: 10/12/2007] [Accepted: 11/01/2007] [Indexed: 12/14/2022] Open
Abstract
Emotional arousal strengthens memory. This is most apparent in aversive conditioning, in which the stress-related neurotransmitter norepinephrine (NE) enhances associations between sensory stimuli and fear-inducing events. In contrast to conditioning, extinction decreases fear responses, and is thought to form a new memory. It is not known, however, whether NE is necessary for extinction learning. Previous work has shown that the infralimbic prefrontal cortex (IL) is a site of extinction consolidation. Here, we show that blocking noradrenergic beta-receptors in IL before extinction training impaired retrieval of extinction the following day, consistent with a weakened extinction memory. We further found that the sequelae of beta-receptor activation, including protein kinase A (PKA), gene transcription and translation in IL, are necessary for extinction. To determine whether activation of this cascade modulates IL excitability, we measured the response of IL pyramidal neurons to injected current. NE increased the excitability of IL neurons in a beta-receptor- and PKA-dependent manner. We suggest that NE released in IL during fear extinction activates a PKA-mediated molecular cascade that strengthens extinction memory. Thus, emotional arousal evoked by conditioned fear paradoxically promotes the subsequent extinction of that fear, thereby ensuring behavioral flexibility.
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Affiliation(s)
- Devin Mueller
- Department of Psychiatry, University of Puerto Rico School of Medicine, San Juan, Puerto Rico.
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Abstract
Endocrinological and Behavioural Effects of Chronic Fluxilan Administration in RatsChronic stress induces changes in the neuroendocrine and neuronal system, including elevation of catecholamines and corticosterone (CORT) levels, and could be an important factor in initial depression. Antidepressants affect monoaminergic neurotransmission and modulate central neuropeptides involved in the coordination of stress response and the control of HPA axis activity. We studied the effects of chronic treatment with fluxilan, a selective inhibitor of serotonin reuptake, in unstressed controls and chronic unpredictable mild stress (CUMS) rats, on behaviour and plasma noradrenaline (NA), adrenaline (A), corticosterone (CORT) and adrenocorticotropic hormone (ACTH). CUMS did not affect plasma NA, A and ACTH, but elevated plasma CORT content. Plasma concentration of catecholamines after fluxilan administration was significantly increased in control and CUMS group. On the other hand, fluxilan expressed no effect on plasma ACTH and CORT concentrations in control animals, but decreased ACTH and CORT levels in CUMS animals. Behaviourally, fluxilan treated animals displayed enhanced anxiety. The results demonstrate that the anxiogenic effects of chronic fluxilan administration are similar to those reported by many other studies. The findings described here suggest that elevated plasma catecholamines may contribute to an adverse effect of this drug on cardiovascular parameters during antidepressant therapy.
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Pawlyk AC, Morrison AR, Ross RJ, Brennan FX. Stress-induced changes in sleep in rodents: models and mechanisms. Neurosci Biobehav Rev 2007; 32:99-117. [PMID: 17764741 PMCID: PMC2215737 DOI: 10.1016/j.neubiorev.2007.06.001] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 05/07/2007] [Accepted: 06/14/2007] [Indexed: 02/04/2023]
Abstract
Psychological stressors have a prominent effect on sleep in general, and rapid eye movement (REM) sleep in particular. Disruptions in sleep are a prominent feature, and potentially even the hallmark, of posttraumatic stress disorder (PTSD) (Ross, R.J., Ball, W.A., Sullivan, K., Caroff, S., 1989. Sleep disturbance as the hallmark of posttraumatic stress disorder. American Journal of Psychiatry 146, 697-707). Animal models are critical in understanding both the causes and potential treatments of psychiatric disorders. The current review describes a number of studies that have focused on the impact of stress on sleep in rodent models. The studies are also in Table 1, summarizing the effects of stress in 4-h blocks in both the light and dark phases. Although mild stress procedures have sometimes produced increases in REM sleep, more intense stressors appear to model the human condition by leading to disruptions in sleep, particularly REM sleep. We also discuss work conducted by our group and others looking at conditioning as a factor in the temporal extension of stress-related sleep disruptions. Finally, we attempt to describe the probable neural mechanisms of the sleep disruptions. A complete understanding of the neural correlates of stress-induced sleep alterations may lead to novel treatments for a variety of debilitating sleep disorders.
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Affiliation(s)
- Aaron C. Pawlyk
- Women’s Health and Musculoskeletal Biology, Wyeth Research, Collegeville, PA 19426 USA
| | - Adrian R. Morrison
- Laboratory for the Study of the Brain in Sleep, Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104 USA
- Center for Sleep and Respiratory Neurobiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104 USA
- Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, PA 19104 USA
| | - Richard J. Ross
- Laboratory for the Study of the Brain in Sleep, Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104 USA
- Center for Sleep and Respiratory Neurobiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104 USA
- Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, PA 19104 USA
- Philadelphia VA Medical Center, Philadelphia, PA 19104 USA
| | - Francis X. Brennan
- Laboratory for the Study of the Brain in Sleep, Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104 USA
- Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, PA 19104 USA
- Philadelphia VA Medical Center, Philadelphia, PA 19104 USA
- * Correspondence: Francis X. Brennan, Ph.D., Medical Research (151), VA Medical Center, 3900 Woodland Ave., Philadelphia, PA 19104.
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